26 



resistant bark, while the inflammable crowns become separated from 

 the ground b}' an ever-increasing clear length of stem. The roots are 

 usually well below the surface, firmly embedded in mineral soil, and 

 out of danger from fires which destroy the superficial-rooted hem- 

 lock, lodgepole pine, spruce, and balsams. 



T\liile fire may be one of the greatest benefits to Douglas fir repro- 

 duction by j)reparing a seed bed, it is also its greatest enemy when 

 once the seedlings are established. Young plants of Douglas fir fall 

 easy victims to fire. The thin, resinous bark and delicate foliage are 

 easily damaged by excessive heat and make a good fuel for the spread 

 of fires. 



Allien they do not actually kill the trees, fires ma}' be the indirect 

 means of their destruction by weakening their power of resistance 

 and by subjecting them to other enemies. By burning away the bark 

 and exposing the wood, fire becomes an agent in introducing destruc- 

 tive insects and fungi. Several insects which infest the roots and 

 lower trimk, together with the common fungous disease called '• butt 

 rot" {Polyporus schv:einitzii) ^ are jDrobably very frequently intro- 

 duced in this way. 



WIND. 



Tlie coast form of Douglas fir is quite subject to windfall, especially 

 when individual trees are left isolated b}' thinning dense stands. This 

 damage is greatly increased by persistent ground fires, which may 

 smoulder in the debris around the base of the trunk until most ot 

 the roots are killed, or the trunk itself so hollowed that it Avill break 

 before the first strong wind. 



Besides the damage from windfall, Douglas fir suffers from inter- 

 nal injury by windshake. This is especially prevalent in Arizona 

 and Xew Mexico, but occurs onh^ in the older timber. It does not 

 menace the life of a tree, except indirectly by preparing a way for 

 the entrance of fungi and a ready path for the disease to spread along 

 the cracks. Windshake often extends far toward the top of the tree 

 and causes serious depreciation in the merchantable quality of the 

 timber. 



FROST. 



The two forms of Douglas fir suffer to a varying degTee from frost. 

 In ver}^ frosty localities with poor drainage, such as the bottoms of 

 narrow ravines and box camions, both forms are susceptible to dam- 

 age from late frosts, especially in earh^ youth, but the coast form 

 is much more likely to be damaged by early frosts, owing to the ten- 

 derness of its fall shoot. Growth in height is undoubtedly often 

 retarded by the killing back of the tender spring growth, and young 



[Cir. 150] 



